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Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93 33.\" $FreeBSD: src/share/man/man4/inet.4,v 1.11.2.6 2001/12/17 11:30:12 ru Exp $ 34.\" $DragonFly: src/share/man/man4/inet.4,v 1.5 2007/07/14 21:48:15 swildner Exp $ 35.\" 36.Dd February 14, 1995 37.Dt INET 4 38.Os 39.Sh NAME 40.Nm inet 41.Nd Internet protocol family 42.Sh SYNOPSIS 43.In sys/types.h 44.In netinet/in.h 45.Sh DESCRIPTION 46The Internet protocol family is a collection of protocols 47layered atop the 48.Em Internet Protocol 49.Pq Tn IP 50transport layer, and utilizing the Internet address format. 51The Internet family provides protocol support for the 52.Dv SOCK_STREAM , SOCK_DGRAM , 53and 54.Dv SOCK_RAW 55socket types; the 56.Dv SOCK_RAW 57interface provides access to the 58.Tn IP 59protocol. 60.Sh ADDRESSING 61Internet addresses are four byte quantities, stored in 62network standard format (on the 63.Tn VAX 64these are word and byte 65reversed). The include file 66.In netinet/in.h 67defines this address 68as a discriminated union. 69.Pp 70Sockets bound to the Internet protocol family utilize 71the following addressing structure, 72.Bd -literal -offset indent 73struct sockaddr_in { 74 u_char sin_len; 75 u_char sin_family; 76 u_short sin_port; 77 struct in_addr sin_addr; 78 char sin_zero[8]; 79}; 80.Ed 81.Pp 82Sockets may be created with the local address 83.Dv INADDR_ANY 84to affect 85.Dq wildcard 86matching on incoming messages. 87The address in a 88.Xr connect 2 89or 90.Xr sendto 2 91call may be given as 92.Dv INADDR_ANY 93to mean 94.Dq this host . 95The distinguished address 96.Dv INADDR_BROADCAST 97is allowed as a shorthand for the broadcast address on the primary 98network if the first network configured supports broadcast. 99.Sh PROTOCOLS 100The Internet protocol family is comprised of 101the 102.Tn IP 103network protocol, Internet Control 104Message Protocol 105.Pq Tn ICMP , 106Internet Group Management Protocol 107.Pq Tn IGMP , 108Transmission Control 109Protocol 110.Pq Tn TCP , 111and User Datagram Protocol 112.Pq Tn UDP . 113.Tn TCP 114is used to support the 115.Dv SOCK_STREAM 116abstraction while 117.Tn UDP 118is used to support the 119.Dv SOCK_DGRAM 120abstraction. A raw interface to 121.Tn IP 122is available 123by creating an Internet socket of type 124.Dv SOCK_RAW . 125The 126.Tn ICMP 127message protocol is accessible from a raw socket. 128.Pp 129The 32-bit Internet address contains both network and host parts. 130However, direct examination of addresses is discouraged. For those 131programs which absolutely need to break addresses into their component 132parts, the following 133.Xr ioctl 2 134commands are provided for a datagram socket in the Internet domain; 135they have the same form as the 136.Dv SIOCIFADDR 137command (see 138.Xr intro 4 ) . 139.Pp 140.Bl -tag -width SIOCSIFNETMASK 141.It Dv SIOCSIFNETMASK 142Set interface network mask. 143The network mask defines the network part of the address; 144if it contains more of the address than the address type would indicate, 145then subnets are in use. 146.It Dv SIOCGIFNETMASK 147Get interface network mask. 148.El 149.Sh ROUTING 150The current implementation of Internet protocols includes some routing-table 151adaptations to provide enhanced caching of certain end-to-end 152information necessary for Transaction TCP and Path MTU Discovery. The 153following changes are the most significant: 154.Bl -enum 155.It 156All IP routes, except those with the 157.Dv RTF_CLONING 158flag and those to multicast destinations, have the 159.Dv RTF_PRCLONING 160flag forcibly enabled (they are thus said to be 161.Dq "protocol cloning" ) . 162.It 163When the last reference to an IP route is dropped, the route is 164examined to determine if it was created by cloning such a route. If 165this is the case, the 166.Dv RTF_PROTO3 167flag is turned on, and the expiration timer is initialized to go off in 168.Va net.inet.ip.rtexpire 169seconds. 170If such a route is re-referenced, the flag and expiration timer are reset. 171.It 172A kernel timeout runs once every ten minutes, or sooner if there are 173soon-to-expire routes in the kernel routing table, and deletes the 174expired routes. 175.El 176.Pp 177A dynamic process is in place to modify the value of 178.Va net.inet.ip.rtexpire 179if the number of cached routes grows too large. 180If after an expiration run there are still more than 181.Va net.inet.ip.rtmaxcache 182unreferenced routes remaining, the rtexpire 183value is multiplied by \(34, and any routes which have longer 184expiration times have those times adjusted. This process is damped 185somewhat by specification of a minimum rtexpire value 186.Va ( net.inet.ip.rtminexpire ) , 187and by restricting the reduction to once in a ten-minute period. 188.Pp 189If some external process deletes the original route from which a 190protocol-cloned route was generated, the ``child route'' is deleted. 191(This is actually a generic mechanism in the routing code support for 192protocol-requested cloning.) 193.Pp 194No attempt is made to manage routes which were not created by protocol 195cloning; these are assumed to be static, under the management of an 196external routing process, or under the management of a link layer 197(e.g., 198.Tn ARP 199for Ethernets). 200.Pp 201Only certain types of network activity will result in the cloning of a 202route using this mechanism. Specifically, those protocols (such as 203.Tn TCP 204and 205.Tn UDP ) 206which themselves cache a long-lasting reference to route for a destination 207will trigger the mechanism; whereas raw 208.Tn IP 209packets, whether locally-generated or forwarded, will not. 210.Ss MIB Variables 211A number of variables are implemented in the net.inet branch of the 212.Xr sysctl 3 213MIB. 214In addition to the variables supported by the transport protocols 215(for which the respective manual pages may be consulted), 216the following general variables are defined: 217.Bl -tag -width IPCTL_FASTFORWARDING 218.It Dv IPCTL_FORWARDING 219.Pq ip.forwarding 220Boolean: enable/disable forwarding of IP packets. 221Defaults to off. 222.It Dv IPCTL_FASTFORWARDING 223.Pq ip.fastforwarding 224Boolean: enable/disable the use of fast IP forwarding code. 225Defaults to off. 226When fast forwarding is enabled, IP packets are forwarded directly to 227the appropriate network interface with a minimal validity checking, which 228greatly improves the throughput. On the other hand, they bypass the 229standard procedures, such as IP option processing and 230.Xr ipfirewall 4 231checking. 232It is not guaranteed that every packet will be fast-forwarded. 233.It Dv IPCTL_SENDREDIRECTS 234.Pq ip.redirect 235Boolean: enable/disable sending of ICMP redirects in response to 236unforwardable 237.Tn IP 238packets. 239Defaults to on. 240.It Dv IPCTL_DEFTTL 241.Pq ip.ttl 242Integer: default time-to-live 243.Pq Dq TTL 244to use for outgoing 245.Tn IP 246packets. 247.It Dv IPCTL_SOURCEROUTE 248.Pq ip.sourceroute 249Boolean: enable/disable forwarding of source-routed IP packets (default false). 250.It Dv IPCTL_RTEXPIRE 251.Pq ip.rtexpire 252Integer: lifetime in seconds of protocol-cloned 253.Tn IP 254routes after the last reference drops (default one hour). This value 255varies dynamically as described above. 256.It Dv IPCTL_RTMINEXPIRE 257.Pq ip.rtminexpire 258Integer: minimum value of ip.rtexpire (default ten seconds). This 259value has no effect on user modifications, but restricts the dynamic 260adaptation described above. 261.It Dv IPCTL_RTMAXCACHE 262.Pq ip.rtmaxcache 263Integer: trigger level of cached, unreferenced, protocol-cloned routes 264which initiates dynamic adaptation (default 128). 265.El 266.Sh SEE ALSO 267.Xr ioctl 2 , 268.Xr socket 2 , 269.Xr sysctl 3 , 270.Xr icmp 4 , 271.Xr intro 4 , 272.Xr ip 4 , 273.Xr ipfirewall 4 , 274.Xr tcp 4 , 275.Xr ttcp 4 , 276.Xr udp 4 277.Rs 278.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 279.%B PS1 280.%N 7 281.Re 282.Rs 283.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 284.%B PS1 285.%N 8 286.Re 287.Sh CAVEAT 288The Internet protocol support is subject to change as 289the Internet protocols develop. Users should not depend 290on details of the current implementation, but rather 291the services exported. 292.Sh HISTORY 293The 294.Nm 295protocol interface appeared in 296.Bx 4.2 . 297The 298.Dq protocol cloning 299code appeared in 300.Fx 2.1 . 301